The present invention relates to a new and novel design for a cage mill for grinding and reducing material such as ore, grain, clay, rock, etc., and particularly to a cage mill which has a stationary and movable housing portion for easy access to and removal of two cooperative cage assemblies from the mill which cage assemblies are mounted on shafts for rotation in opposite directions.
Several major problems are inherent in the designs of past cage mills as exemplified in U.S. Pat. Nos. 3,028,105; 3,047,243; and 3,503,561. First, the housings of the cage mills consist of several pieces joined together thus requiring a large number of complex sealing joints to be maintained to keep dust from escaping from the grinding chamber. In addition, the main drive motors and drives are located remotely from the cage mill, thereby requiring a disassembly of the V-belts and guards from the main drive motors when the movable side of the housing is retracted from the stationary side. It is therefore, an object of the present invention to substantially reduce downtime of the machine, more particularly separating the housing to allow access to cages and other internal members, without requiring any disconnecting of drive components.
It is another object of the present invention to provide a simplified construction for the cage mill housing consisting of a movable and a stationary portion and requiring a sealing between only these two components, and permitting easy retraction of the movable portion since the main drive motors and drives are mounted on the pedestal of the movable portion for movement therewith.
Another object of the present invention is to provide a substantially continuous sealing arrangement located externally around the perimeter of the housing where the movable and stationary portions come together, and consisting of a rigid lip which is engaged deeply into a cross-sectional area of a pliable material to always maintain a positive sealing condition, yet allowing for any misalignment which may exist between the two housing portions.
Secondly, in the cage mill designs of U.S. Pat. Nos. 3,028,105 and 3,503,561, the mounting of a cage assembly or rotor on a shaft is done by bolting the cage assembly to a hub mounted on the shaft. The hub has a bolting flange and a machined shoulder to which the cage is fitted. Since the cage assemblies and hub are exposed to the environment of the grinding chamber, corrosion normally occurs between the cage bore and the machined shoulder on the hub, making cage assembly removal for replacement or repair of any components in the housing chamber very difficult and time-consuming.
It is therefore a further object of the present invention to provide a means for easily securing and releasing the cage assembly from the hub and shaft, thereby reducing the time and eliminating the difficulty involved when removing and replacing the cage assemblies in the mill.
More particularly, a tapered nut element is used to expand a heat treated steel split ring into the bore of the cage assemblies and hub, thus holding the cage assembly centered with and against the face of the hub. Removal of the nut element causes the split ring to contract, thereby releasing the cage assembly from the hub.
Thirdly, the impact members of the cages in U.S. Pat. Nos. 3,028,105 and 3,503,561 are the same length in rows 2 and 3 radially outwardly from the axis of the shafts, which means that the ring supporting one end of the members are located in the path of the material to be pulverized. Consequently, the rings are subjected to severe abrasion. To combat this problem these patents disclose the use of rolled bands of steel, each band located at the periphery of a row of sleeves and welded to the adjacent disk in order to protect the ring of the next row. However, the band is relatively thin due to limitation of space in the area where the band is located, consequently abrasion of the rings still occurs resulting in a very short service life of the band.
A still further object, therefore, of the present invention is to provide permanent protection against abrasion for the cage rings, and more importantly, a increase in the pulverizing efficiency of the cage mill.
More particularly, the two primary disks to which the impact members are connected are of a stepped configuration providing an offset for receiving the rings of the next row. By increasing the axial length of the impact members of the second, third, and fourth rows, the cage rings of rows 2 and 3 are nested in the offsets. This provides protection of the ring against abrasion and creates a smooth flow path for the material passing through the cages.
Another object of the present invention is to provide a means for achieving a nested relationship of the rings of one cage assembly in the offsets formed by the other cage assembly. This means involves axial movement of the shaft to which the cage assembly is mounted.
The newly established increased axial length of the impact members increases the cross sectional area of the space between rows. This affords the material more space to which to be disbursed, thereby providing improved impacting conditions.